Normal sol-gel processes utilize a metal oxide or hydroxide sol that is obtained from an inorganic compound solution, an organic metal compound solution of a metal alkoxide, or a similar compound. The sol is then gelled, and the gel is heated to produce a ceramic or glass.
Silica (SiO2) glass production processes using sol-gel processes are known. Numerous examples are described by S. Sakka in the book Sol Gel Science, which was published by Agune Shofu Publishing. Most sol-gel processes are for the production of films less than 1 μm (micrometer) thick and use a metal alkoxide solution for integral formation on a base such as glass or a conductor. Although bulk type SiO2 glass formed using a sol-gel process have been prepared separately and independently of a base, special drying machines (e.g., drying machines for supercritical drying) have been used to prevent the occurrences of cracks during the drying step. If the special drying equipment is not utilized, the drying must be carried out very slowly. For example, Japanese Unexamined Patent Publication SHO No. 61-236619 describes a production process for quartz glass using a sol-gel process. The drying method involves maintaining the film overnight at 20° C. and then using a container cover with a prescribed opening ratio for drying at 60° C. for 10 days. Similarly, Japanese Unexamined Patent Publication HEI No. 4-292425 describes a production process for silica glass using a sol-gel process. The starting sol is placed in a dish, gelled at room temperature, and then the cover of the dish is replaced with one containing holes for drying at 60° C. for 100 days. Such prolonged drying is considered a major obstacle for production via these methods.
Furthermore, bulk type SiO2 glass produced by conventional sol-gel processes generally have a thickness of several tens of millimeters or greater. Methods for producing self-supporting glass films are therefore of interest.